High Intensity Discharge (HID) lamps have been manufactured in a variety of envelope (jacket) shapes and sizes. These lamps generally comprise jackets suited to particular applications. Some metal halide lamps are referred to as being double ended. This relates to the fact that the arc tube is held within a tubular-like outer jacket or sleeve, and each end of the outer jacket has a base member. The arc tube that is the subject of this invention is double ended and is enclosed within a sealed jacket and has one lead connected to each end of the jacket, thereby being securely held in place within the jacket. The jacket, in turn, is held in place by fixture connections. These connections supply the electrical energy required for the discharge capsule (arc tube), and also provide means of physical support for the lamp.
The more common type of HID lamp has been the single end type of lamp, such as Model Nos. ED17, BT37, etc., manufactured by the present assignee, Osram-Sylvania. The lamp consists of a quartz tube (and other ancillary components) within a glass envelope. The envelope has a base attached to one end. The base is the means of transferring electric power to the arc capsule and is also the means of physical support for the whole lamp. The arc discharge capsule is rigidly supported, within the glass envelope, to a flare stem at the base region.
It has been common practice to add hardware to support the arc tube mount assembly. These added parts make use of the opposite (base) end of the glass envelope to secure the mount assembly rigidly, so that it will withstand the rigors of handling and shipping. Methods of securing the other end within the glass envelope range from spring-like members that exert a force against the glass envelope interior to other types of glass envelopes that have "dimples" or protuberances molded into them at the opposite (base) end. Portions of the mount assembly can be secured to these molded pieces by fitting them either into, or around, the protrusions. This secures the components and assures the structural integrity of the lamp.
More recently, metal halide lamps have utilized a "shroud" or other means that surround the arc discharge capsule. This shroud is, consequently, a part of the mount structure. It is believed that this enclosure may contribute to the thermal stability of the arc tube operation. The shroud may also be utilized as a means of providing an infrared reflecting surface in order to improve the efficacy of the lamp. It also may be used to reduce the amount of transmitted ultraviolet radiation, or may be used to improve the containment characteristics of a lamp, particularly during arc tube rupture.
Unfortunately this shroud enclosure contributes weight to the mount assembly. The added weight, in turn, increases the possibility of dislocating or shifting the position of the assembly during handling and shipping.
A recent metal halide arc discharge lamp design manufactured by the present assignee utilizes a formed arc tube disposed within a hermetically sealed aluminosilicate inner jacket. This assembly is housed within a bonded lens reflector jacket.
This configuration poses an interesting conundrum. On one hand, exacting demands are placed on the manufacturing processes needed to fabricate this product; and on the other hand, the design provides an opportunity for a new, unique high efficacy light source with good color temperature and excellent color rendering index. This design also has the advantage of being directed, owing to its being in a reflector outer jacket.
The process of fabricating this bonded lens metal halide lamp consists of a series of steps. Glassware is received without eyelets in the heel, or a lens on the reflector. It has not been aluminized and obviously does not contain a light source. The glassware is processed to accept and secure eyelets through the heel region. The interior surface of the glassware is then coated with a vapor-deposited layer of aluminum (reflective surface). The light source is then inserted into the now aluminized glassware, and bonded to the attached eyelets to ensure mechanical strength and electrical contact. The entire unit is further processed to bond the lens to the reflector. The very nature of this process precludes any method of allowing a capsule or arc tube mount assembly that is bonded to the eyelets, from being secured to the opposite (lens) end.
A similar mount assembly of considerable mass, secured at only one end, is illustrated in U.S. Pat. No. 5,043,623, issued to Scholz et al, and entitled REFLECTOR LAMP ASSEMBLY INCLUDING METAL HALIDE ARC TUBE. The patent teaches a design wherein an electrically-isolated support ring located in the heel region of the reflector is attached to the connecting rod of the mount structure. The mounting assembly of this invention cannot utilize those teachings, owing to the lack of electrically-isolated mounting components, such as a connecting rod, to secure the ring support in order to provide mount structural integrity without sacrificing lamp performance.
One of the inherent difficulties with such mounting assemblies is the physical size and mass of the inner jacket mount. The HID lamp of this invention is a factor of two larger in "glass length", and a factor of five higher in weight, than are similar halogen capsule mountings. These increases exert additional stress upon the single-ended mount within the reflector of the inventive assembly.
The use of butt welding improved the strength of the inner jacket press region, but was not sufficient to survive the rigors associated with lamp shipping and dropping. A rigid length of molybdenum wire (0.020" dia.) was recently utilized to connect from one eyelet to the top of the mount structure. However, owing to the overall length of the mount, the mount structure flexed considerably during shipping and handling. This flexing produced leverage and high levels of stress on the press region, which resulted in the cracking of the press.
Work-hardened nickel (0.035" dia.) was also tried, but flexing and mount movement still resulted in press cracking.
The present mounting assembly of this invention provides additional stability and rigidity for the mount of a reflector lamp. The invention improves the strength of the mount structure and additionally limits mount movement. This reduces the leveraged stress to the press region of the inner jacket.
This improvement also substantially reduces or eliminates the flexure-induced press cracking previously encountered.
A further advantage of using the spiral mount of the present invention is an unexpected enhancement of the lamp-starting characteristics.